1. Field of the Invention
The present invention relates to a lens system, and more particularly to a miniaturized, high performance, and low price zoom lens system that can ensure a good optical performance.
2. Description of the Prior Art
Since the image taking lens system has an increasingly wide range of application, particularly for the mobile phone, the image taking has become one of the necessary functions. Nowadays, a mobile phone is usually equipped with a solid image sensor and an image taking lens system, such as CCD sensor (charge coupled device) or CMOS sensor (Complementary Metal Oxide Semiconductor). To comply with the requirement of miniaturizing the solid image sensor and the image taking lens system as well as improving the performance thereof, four-piece lens system in the products needs to be miniaturized and its performance thereof also needs to be improved. Therefore, with the popularization of photographic mobile phone, the research and development of the whole group focusing structure is becoming more and more urgent. Hence, how to develop a whole group focusing structure more satisfying the user's requirements has become an important consideration of the manufacturer.
With the advancement of CCD image sensing technology in recent years, the lens taking system is developing toward high density and high definition, and accordingly, its optical performance is required to be improved. Besides, the zoom lens used in digital camera and mobile phone is also required to be more miniaturized, low priced, and light weighted. If want to double the zoom ratio of the zoom lens system, it requires that the number of the lens units is small and the performance of the lens units should be high. An ordinary zoom lens generally comprises a negative refractive first lens group and a positive refractive second lens group arranged sequentially from the object side, and the focal length changes with the distance between the lens groups. It is well known that the structure of the second lens group is comparatively simple, and the following patent documents disclose the similar lens systems:
Patent document No. 1 (JP Pt 11183616), Patent document No. 2 (JP Pt 446308), Patent document No. 3 (JP Pt 446310), Patent document No. 4 (JP Pt 456814).
Patent document No. 1 discloses an optical system comprising five lens units (first lens group consisted of two lens units and second lens group has three lens units), the optical system is miniaturized and low priced with the use of spherical lens units. However, the distance between the spherical lens units is very difficult to adjust (optical performance adjustment), it is difficult for the manufacturers to find the proper structural arrangement.
Patent Nos. 2–4 achieve miniaturization and high performance by the use of several spherical lens units, their optical performance can be adjusted easily, however, the Fno.4.6 at the wide angle end will become comparatively dark, and the use of spherical glass will increase the production cost.
To solve the abovementioned problems, and based on many years of experiences and technologies accumulated in the optical lens system field, the applicant has developed a miniaturized, high performance, and low price zoom lens system, wherein the refractive power of the respective lens groups is evenly distributed and the lens unit shape is appropriate.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.